Lecture 1 on Pharmacology PDF

Lecture 1 pharmacology General pharmacology Pharmacology: Branch of science that deals with drugs. Subdivisions of Pharmacology P...

Lecture 1 pharmacology General pharmacology Pharmacology: Branch of science that deals with drugs. Subdivisions of Pharmacology Pharmacokinetics (ADME) Pharmacodynamic (effect of the body on the drug) (effect of the drug on the body) Pharmacokinetics def effect of the body on the drug phases 1) Absorption 2) Distribution 3) Metabolism 4) Excretion importance Tailor a dose regimen to the individual requirements of a patients (e.g., patients of renal failure and liver disease). Find out a possible cause of treatment failure. (Drug can not reach site of action or taken by wrong route) Find out the cause of drug toxicity. I- Absorption Definition Transfer of drug from site of administration to blood stream. Factors A. Factors related to the drug B. Factors related to the patient affecting Lipid solubility: lipid soluble drugs are more Route of administration: I.V is the drug readily absorbed. faster. absorption: Degree of ionization; the greater the lesser Absorbing surface area. the absorption. Specific factors: Intrinsic factor is Stability of gastric acid and digestive needed for Vitamin B12 absorption. enzymes (benzyl- penicillin and insulin are destroyed in GIT). Effect of PH and Pka on drug ionization and lipid solubility 1 Dr Mohammed Saad NMU  Lecture 1 pharmacology pH, pKa and drug ionization: def pKa is the pH at which 50% of the drug is ionized and 50% is unionized e.g.: Pka of aspirin 3.5. Pka (of the drug) = PH (of the media) + log unionized /Ionized. principle Unionized drugs (uncharged) are more lipid soluble and more easily absorbed and vice versa Most drugs are weak acids or bases. Weak acids are better absorbed in acidic media where it is less ionized and so more lipid soluble. Weak bases are better absorbed in alkaline media where it is less ionized and so more lipid soluble. example Aspirin is an acidic drug with Pka 3.5, this means in media with PH 3.5 aspirin will be half ionized, and half unionized. The more the acidic medium the more the absorption of aspirin and vice versa. Clinical 1) Knowing site of drug absorption: significance Acidic drugs as aspirin are largely unionized in gastric acidic PH and are absorbed from of stomach While bases, e.g., atropine are largely ionized and are absorbed only when they reach the intestines. 2) Ion trapping: Acidic drugs as aspirin are largely unionized in gastric lumen, which is acidic, so aspirin passes into cells lining stomach. But once entered cells find the pH is alkaline where it is ionized and trapped 3) Treatment of drug toxicity: Alkalization of urine decreases renal reabsorption, so increase renal excretion of acid drugs. e.g., Aspirin. Acidification of urine increase renal excretion of basic drugs. First pass metabolism (presystolic elimination): def Metabolism of drugs in site of administration before reaching systemic circulation. e.g., GIT or liver after oral administration. types Gut first pass effect: Hepatic first pass effect: Gastric acidity: destroys benzyl penicillin As Nitroglycerine Digestive enzymes: destroy insulin. To avoid high first change the route of drug administration. ex, Give nitroglycerine sublingual. pass effect: increase the oral dose. Bioavailability: def It is the fraction of the drug that reaches the systemic circulation in the unchanged form. example Bioavailability is 100% after IV administration. Variable after oral administration. For example, if 100 mg of a drug are administered orally and 70 mg of this drug are absorbed unchanged, the bioavailability of this drug is 70%. Factors 1) Absorption: The more the drug absorption the higher the bioavailability affecting it 2) First pass metabolism: The more first pass metabolism, the less the bioavailability 2 Dr Mohammed Saad NMU